Former world number one Jordan Spieth said he would not be surprised if this week's US PGA Championship winner Phil Mickelson had another major title in him.
Mickelson, 50, made history as the oldest major winner on Sunday when he triumphed at the US PGA Championship at Kiawah Island in South Carolina, claiming his sixth career major title.
The American's major victory in the twilight of his career was similar to golf greats Tiger Woods at the 2019 Masters and Jack Nicklaus at the 1986 Masters.
Spieth was full of praise for his childhood hero and long-time mentor, when speaking ahead of this week's Charles Schwab Challenge at the Colonial Country Club in Texas.
"It seems like all the great ones have that one left at the end," Spieth said.
"I know he'll probably tell you, he thinks he's got more than one left. I don't think anybody will doubt him after this one, but I think it's just wild. I think it's incredible."
The 27-year-old, who has won three major titles, said he watched on in awe as Mickelson triumphed on Sunday for his first major victory since 2013.
"I thought it would be very, very difficult," Spieth said. "He hadn't been in contention in quite a while on the PGA Tour against the guys he was in contention with.
"I know he's won many times on the Champions Tour… I think that might have been something that had been helpful for him as he's coming down the stretch.
"It's just so difficult to be in contention for the first time in a while and be able to tap into that confidence that you're supposed to be there and you're supposed to win."
Spieth's career skyrocketed after playing alongside Mickelson at the 2013 Deutsche Bank Championship where he shot a final-round 62. That round prompted Mickelson to call US Presidents Cup Captain Fred Couples to insist on calling up Spieth.
The Texan has long held an adoration for Mickelson, revealing he had got his prized signature in his youth. That adoration has been further reinforced by the recent fears of Mickelson, 23 years Spieth's senior.
"His streak of not being outside the top 50 in the world for however long, that is going to be a very difficult task for anybody going forward to match," Spieth said.
"Then to win a tournament, let alone a major championship, at 50 with how young and stacked the game has gotten is just an incredible feat.
"I think the way he handled Saturday and Sunday, when he did make mistakes - especially on the back nine on Saturday to then close that out and remain in the lead - it was typical Phil."